1. Technical Field
The present invention relates to a traction control system for a vehicle which banks while rounding a curve and also relates to a saddled vehicle including such a control system.
2. Description of the Related Art
Some people proposed providing a motorcycle with a traction control system which controls the engine power so that predetermined driving force can be obtained with the rear wheel prevented from slipping excessively. In performing the traction control, the rear wheel's slipping is detected and the engine's driving force is reduced according to the magnitude of that slipping, thereby minimizing slipping.
Particularly when driving a motorcycle around a curve, the rider is required to twist the accelerator grip finely. That is why to lighten the rider's operation load, some people say the traction control should work. For example, Japanese Laid-Open Patent Publication No. 2010-285987 teaches changing the slip value to be a threshold value at which the traction control should be started according to the bank angle of a motorcycle.
As long as the motorcycle is running at a small bank angle, the permissible slip value is so large that relatively light operation load is imposed on the rider. For that reason, until the slip value reaches a certain level, there is only a little need to lighten the rider's operation load by performing the traction control. However, if the motorcycle is running at a large bank angle, the permissible slip value is so small that heavy operation load is imposed on the rider. In that case, there is a lot of need to lighten the rider's operation load by performing the traction control when the slip value is still small.
However, the present inventors discovered and confirmed via experiments that just by changing the slip value to be a threshold value at which the traction control should be started according to bank angle so that the threshold slip value becomes small if the bank angle is large but becomes large if the bank angle is small, the rider's operation load could not be lightened sufficiently in some cases. The reason is as follows. Specifically, when a motorcycle is rounding a curve, the magnitude of the bank angle is almost the same irrespective of the radius of curvature R of that curve. Nevertheless, according to the radius of curvature R of the curve, the rider needs to change the accelerator position when entering the latter half of curve, and the rate of increase in slipping, if any, also changes. And if the rate of increase in slipping is high, the traction control should be started as easily as possible. Consequently, the present inventors discovered that there is room for further lightening the rider's operation load by changing the facility to start the traction control according to the radius of curvature R of the curve.
The present invention provides a traction control system which contributes to further lightening the operation load on a rider who is driving a motorcycle around a curve and also provides a saddled vehicle including such a control system.